In-situ hydroisomerization of synthesized hydrocarbon liquid in a slurry fischer-tropsch reactor

ABSTRACT

A slurry Fischer-Tropsch hydrocarbon synthesis process for synthesizing liquid hydrocarbons from synthesis gas in a hydrocarbon synthesis reactor also hydroisomerizes the synthesized hydrocarbon liquid, which comprises the slurry liquid, in one or more downcomer reactors immersed in the slurry body in the synthesis reactor. A monolithic catalyst is preferably used for the hydroisomerization, and slurry circulation down through the downcomer reactors from the surrounding slurry body, is achieved at least in part by density-difference driven hydraulics created by removing gas bubbles from the slurry passed into the downcomers. Preferably, catalyst particles are also removed before the slurry contacts the catalyst. Hydroisomerization occurs while the synthesis reactor is producing hydrocarbons, without interfering with the hydrocarbon synthesis reaction.

BACKGROUND OF THE DISCLOSURE

1. Field of the Invention

The invention relates to a slurry hydrocarbon synthesis process withhydrocarbon hydroisomerization in the synthesis reactor. Moreparticularly the invention relates to a slurry Fischer-Tropschhydrocarbon synthesis process, wherein the synthesized hydrocarbonslurry liquid is hydroisomerized in the synthesis reactor by circulatingit down through a downcomer reactor in the synthesis slurry, in whichthe liquid reacts with hydrogen in the presence of a monolithichydroisomerization catalyst.

2. Background of the Invention

The slurry Fischer-Tropsch hydrocarbon synthesis process is now wellknown and documented, both in patents and in the technical literature.This process comprises passing a synthesis gas, which comprises amixture of H₂ and CO, up into a hot reactive slurry in a hydrocarbonsynthesis reactor, in which the slurry comprises synthesizedhydrocarbons which are liquid at the synthesis reaction conditions andin which is dispersed a particulate Fischer-Tropsch type of catalyst.The H₂ and CO react in the presence of the catalyst and formhydrocarbons. The hydrocarbon liquid is continuously or intermittentlywithdrawn from the synthesis reactor and pipelined to one or moredownstream upgrading operations. The upgraded products may include, forexample, a syncrude, various fuels and lubricating oil fractions andwax. The downstream upgrading includes fractionation and conversionoperations, typically comprising hydroisomerization, in which a portionof the molecular structure of at least some the hydrocarbon molecules ischanged. It would be an improvement if the synthesized hydrocarbonslurry liquid could be at least partially hydroisomerized to reduce itspour and melt points within the synthesis reactor and without the needfor a separate hydroisomerization facility, to make it moretransportable by pipeline, before it is transferred to downstreamoperations.

SUMMARY OF THE INVENTION

The invention relates to a slurry Fischer-Tropsch hydrocarbon synthesisprocess in which the synthesized hydrocarbon slurry liquid ishydroisomerized in the synthesis reactor by circulating it down throughone or more downcomer reactors in the synthesis slurry, in which theliquid reacts with hydrogen in the presence of a hydroisomerizationcatalyst and preferably a monolithic hydroisomerization catalyst, tohydroisomerize the liquid which is then passed back into the slurry bodyin the synthesis reactor. The slurry liquid, which comprises synthesizedhydrocarbons that are liquid at the synthesis reaction conditions,comprises mostly normal paraffins and the hydroisomerization reduces itspour and melt points, thereby making it more pumpable and pipelinable.By downcomer reactor is meant a downcomer containing thehydroisomerization catalyst in its interior and that circulation ofslurry from the slurry body down through the downcomer reactor isproduced all or mostly by density-difference hydraulics, in which thedensity of the slurry flowing down through the downcomer reactor isgreater than the surrounding slurry body in the synthesis reactor.Slurry densification is achieved by removing at least a portion of thegas bubbles from the slurry, thereby densifying it before it passes downthe downcomer reactor. The one or more downcomer reactors may eachcomprise a simple, substantially vertical, hollow fluid conduit or pipeopen at its top and bottom and are immersed in the slurry body in thesynthesis reactor. Except for the absence of a hydroisomerizationcatalyst and means for injecting a hydrogen treat gas into its interior,the simple type of downcomer having a slurry gas bubble removing meansat it top disclosed in U.S. Pat. No. 5,382,748 the disclosure of whichis incorporated herein by reference, is an example of means which can bemodified to be useful as a downcomer reactor in the process of theinvention.

The process comprises contacting hot slurry from the slurry body in thesynthesis reactor with means for removing gas bubbles, and preferablygas bubbles and at least a portion of the particulate solids from theslurry liquid which densifies it, with the densified slurry and ahydrogen treat gas passed into the interior of the one or more downcomerreactors and then back into the surrounding slurry body. Thehydroisomerization catalyst is located in the interior of the downcomerreactor and comprises the hydroisomerization reaction zone, in which thehydrogen reacts with the slurry hydrocarbon liquid to hydroisomerize atleast a portion of it and produce a hydroisomerized liquid of reducedpour point. The hydroisomerized hydrocarbon liquid of reduced pour pointthen passes out of the downcomer and back into the surrounding slurrybody in the synthesis reactor. This enables hydroisomerizing the slurryliquid (i) inside the synthesis reactor and (ii) while the synthesisreactor is producing hydrocarbons, but without interfering with thehydrocarbon synthesis reaction. The concentration of hydroisomerizedhydrocarbon liquid in the synthesis reactor continues to increase untilequilibrium conditions are reached. When the reactor reaches equilibriumit is possible for the slurry liquid being removed from it to comprisemostly hydroisomerized hydrocarbons of reduced pour point. In somecases, no further hydroisomerization of the liquid hydrocarbon productwithdrawn from the synthesis reactor is necessary. Thus, the process ofthe invention will reduce and in some cases even eliminate the need fora separate, stand-alone hydroisomerization reactor and associatedequipment downstream of the synthesis reactor. If a downstreamhydroisomerization reactor is needed, it will be smaller than it wouldbe if the synthesized hydrocarbon liquid passed into it was not at leastpartially hydroisomerized. While all of the hydroisomerized hydrocarbonliquid is typically returned back into the surrounding slurry body inthe synthesis reactor with which it mixes, in some embodiments a portionof the hydroisomerized liquid may be passed from the downcomer reactor,out of the syntheses reactor to downstream operations.

The gas bubble and preferably the slurry gas bubble and particulatesolids removal means is also located in the slurry body in the synthesisreactor and may comprise the same or separate means. While variousfiltration means may be used to separate the slurry liquid from at leasta portion of the catalyst and any other particles, before the slurry ispassed down into the hydroisomerization zone, in the practice of theinvention the use of filtration means may be avoided by using knownslurry solids reducing means that do not is employ filtration. Gasbubble and solids removal means suitable for use with the presentinvention are known and disclosed in, for example, U.S. Pat. Nos.5,866,621 and 5,962,537, the disclosures of which are incorporatedherein by reference. In addition to the '748 patent referred to above,simple gas bubble removing means are also disclosed in U.S. Pat. Nos.5,811,468 and 5,817,702, the disclosures of which are also incorporatedherein by reference. While gas bubble and solids removal means may ormay not be part of the downcomer reactor, in these four patents the gasbubble and the gas bubble and solids removal means are immersed in theslurry body and comprise the slurry entrance at the top of thedowncomer. As mentioned above, removing gas bubbles from the slurrydensifies it and, if properly employed in connection with feeding itdown into and through the downcomer reactor (e.g., the slurry isdensified sufficiently above the external hydroisomerization zone),provides a density-difference driven hydraulic head to circulate theslurry from the slurry body in the synthesis reactor, down into andthrough the internal downcomer reactor and back into the surroundingslurry body. Removing gas bubbles from the slurry prior tohydroisomerization also reduces the CO and water vapor content of theflowing fluid, which could otherwise react with the hydroisomerizationhydrogen and also adversely effect the hydroisomerization catalyst. Amonolithic hydroisomerization catalyst having substantially verticalfluid flow channels and a minimal solid cross-sectional areaperpendicular to the flow direction of the fluid minimizes the pressuredrop of the fluid flowing down and across the catalyst surface. Removingcatalyst and other solid particles, such as inert heat transferparticles, from the slurry upstream of the hydroisomerization zone,reduces scouring of the monolithic catalyst and plugging of thehydroisomerization reaction zone.

The invention comprises a slurry Fischer-Tropsch hydrocarbon synthesesprocess in which synthesized hydrocarbon slurry liquid ishydroisomerized in the synthesis reactor during hydrocarbon synthesis,by circulating slurry from the slurry body in the synthesis reactor downthrough a hydroisomerization zone in a downcomer reactor immersed in theslurry body, in which the slurry hydrocarbon liquid reacts with hydrogenin the presence of a hydroisomerization catalyst. Slurry circulationbetween the downcomer reactor and slurry body is achieved by thedensification resulting from the gas bubble removal. At least a portionof the slurry liquid is hydroisomerized and this reduces its pour point.The hydroisomerized slurry leaves the downcomer reactor and all or mostof it passes back into the surrounding slurry body with which it mixes.Preferably the hydroisomerization catalyst comprises a monolithiccatalyst and at least a portion of both solids and gas bubbles areremoved from the slurry before it contacts the hydroisomerizationcatalyst. More specifically the invention comprises a hydrocarbonsynthesis process which includes hydroisomerizing hydrocarbon liquidproduced by the synthesis reaction while the hydrocarbon liquid is beingproduced from a synthesis gas, the process comprising the steps of:

(a) passing a synthesis gas comprising a mixture of H₂ and CO into aslurry body comprising a three-phase slurry in a slurry Fischer-Tropschhydrocarbon synthesis reactor, in which the slurry comprises gas bubblesand a particulate hydrocarbon synthesis catalyst in a slurry hydrocarbonliquid;

(b) reacting the H₂ and CO in the presence of the catalyst at reactionconditions effective to form hydrocarbons, a portion of which are liquidat the reaction conditions and comprise the slurry hydrocarbon liquid;

(c) contacting a portion of the slurry from the slurry body with meansfor removing gas bubbles, to form a densified slurry reduced in gasbubbles whose density is greater than that of the slurry comprising theslurry body in the synthesis reactor;

(d) passing a hydrogen treat gas and the densified slurry into ahydroisomerizing zone in one or more downcomer reactors immersed in theslurry body in the synthesis reactor, in which the hydrogen andhydrocarbon slurry liquid react in the presence of a preferablymonolithic hydroisomerization catalyst to form a hydrocarbon liquid ofreduced pour point, and

(e) passing all or a portion of the pour point reduced liquid back intothe surrounding slurry body.

While the liquid is being synthesized and hydroisomerized in thesynthesis reactor, a portion is continuously or intermittently withdrawnand sent to downstream operations. It is preferred that at least aportion, and more preferably as much as possible of the particulatesolids are removed from the slurry, before it is passed down into thehydroisomerizing zone.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a simple schematic flow diagram of a hydrocarbon synthesisreactor containing a hydroisomerization zone within, according to oneembodiment of the invention.

FIG. 2 is a plot of hexadecane conversion as a function of temperaturein the presence of a monolithic hydroisomerization catalyst in a pilotplant tubular reactor.

FIG. 3 is a graph illustrating hexadecane hydroisomerization selectivityover a monolithic hydroisomerization catalyst in a pilot plant tubularreactor.

DETAILED DESCRIPTION

The waxy slurry liquid synthesized in the hydrocarbon synthesis reactorwill typically comprise 500° F.+ hydrocarbons, with most having aninitial boiling point in the 650-750° F.+ range. The end boiling pointwill be at least 850° F., preferably at least 1050° F. and even higher(1050° F.+). This liquid also comprises mostly (more than 50 wt. %),typically more than 90%, preferably more than 95% and more preferablymore than 98 wt. % paraffinic hydrocarbons, most of which are normalparaffins, and this is what is meant by “paraffinic” in the context ofthe invention, particularly when the hydrocarbon synthesis catalystcomprises a cobalt catalytic component. The exact boiling range,hydrocarbon composition, etc, are determined by the catalyst and processvariables used for the synthesis. It has negligible amounts of sulfurand nitrogen compounds (e.g., less than 1 wppm). Slurry liquids havingthese properties and useful in the process of the invention have beenmade using a slurry Fischer-Tropsch process with a catalyst having acatalytic cobalt component. In the practice of the invention, it ispreferred that the slurry Fischer-Tropsch hydrocarbon synthesis catalystcomprise a catalytic cobalt or iron component. It is also preferred thatthe synthesis reaction have a Schulz-Flory alpha of at least 0.90, ashigher molecular weight hydrocarbons are preferred in most cases. Thegas bubbles in the slurry comprise synthesis gas, vapor and gaseousproducts of the synthesis reaction, such as C₁-C₄ hydrocarbons, andespecially methane, CO₂ and water vapor. The hydroisomerization catalystis adversely effected by water vapor. Therefore, in addition todensifying the slurry, gas bubble removal is also beneficial to thedownstream hydroisomerizing catalyst. The flow rate of a gasbubble-reduced slurry down through a vertical downcomer can besubstantial and a high flow rate is desired to offset the lift action ofthe hydrogen treat gas injected into the hydroisomerizing zone in thedowncomer reactor. A high liquid flow rate prevents the hydrogen treatgas from pushing the downflowing slurry back up and out of the downcomerreactor, it also prevents the gas from rising up and out of thehydroisomerization zone, before hydroisomerization can take place. In anexperiment with a 30 foot tall slurry hydrocarbon synthesis reactor,using a simple gas disengaging cup on top of a vertical downcomer pipeof the type disclosed in U.S. Pat. No. 5,382,748, resulted in a 12ft/sec liquid flow rate down a 3 inch downcomer pipe, from which onlyhalf of the 60 vol. % of gas bubbles had been removed.

The hydroisomerization catalyst will have a both ahydrogenation/dehydrogenation function and an acid hydrocrackingfunction for hydroisomerizing the normal paraffinic hydrocarbons in theslurry hydrocarbon liquid. The hydrocracking functionality of thecatalyst results in the conversion of some of the waxy slurry liquid tolower boiling material. Since the hydroisomerization zone is in thehydrocarbon synthesis reactor, the hydroisomerization temperature andpressure will be substantially the same as that in the hydrocarbonsynthesis reactor, unless means are employed to heat or cool the gasreduced slurry passing down the downcomer reactor. Thus, whilehydroisomerization is broadly achieved at reaction temperatures rangingfrom 300-900° F. and preferably 550-750° F., the temperature in a slurryhydrocarbon synthesis reactor will typically range from 320-600° F. Thepressure in the hydroisomerization zone will be substantially the sameas that in the synthesis reactor, which is about 80-600 psig. However,U.S. Pat. No. 5,268,344, the disclosure of which is incorporated hereinby reference, discloses means for adjusting the temperature in avertical catalyst rejuvenation draft tube immersed in the slurry in ahydrocarbon synthesis reactor and these means may also be used to adjustthe temperature in the interior of the downcomer reactor in the practiceof the present invention. However, this will mean that the heat exchangemeans in the slurry synthesis reactor used to remove some of theexothermic heat of the synthesis reaction, will also have to remove theadditional heat added in the hydroisomerization zones(s), in the case ofheat addition into these zones to increase the hydroisomerizationtemperature above that of the synthesis temperature. This may not befeasible or desirable. The hydrogen treat gas rate will be from 500-5000SCF/B, with a preferred range of 2000-4000 SCF/B. By hydrogen treat gasis meant all hydrogen or preferably at least about 60 vol. % hydrogenand an inert diluent gas, such as argon or methane. Excess hydrogen isemployed during the hydroisomerization to insure an adequate hydrogenpartial pressure and to prevent any CO remaining in the downflowingslurry from adversely effecting the hydroisomerization reaction andcatalyst. The hydroisomerization catalyst comprises one or more GroupVIII catalytic metal components supported on an acidic metal oxidesupport to give the catalyst both a hydrogenation function and an acidfunction for hydroisomerizing the hydrocarbons. At relatively lowerhydroisomerizing temperatures, such as the temperature in the slurryhydrocarbon synthesis reactor, the catalytic metal component willtypically comprise a Group VIII noble metal, such as Pt or Pd, andpreferably Pt. However, if means are employed in the practice of theinvention to raise the temperature in the hydroisomerization zone tosufficiently high levels, it will typically be preferred that thecatalytic metal component comprise one or more less expensive non-nobleGroup VIII metals, such as Co, Ni and Fe, which will typically alsoinclude a Group VIB metal (e.g., Mo or W) oxide promoter. Irrespectiveof which Group VIII metal component is used, the catalyst may also havea Group IB metal, such as copper, as a hydrogenolysis suppressant. TheGroups referred to herein refer to Groups as found in the Sargent-WelchPeriodic Table of the Elements copyrighted in 1968 by the Sargent-WelchScientific Company. The cracking and hydrogenating activity of thecatalyst is determined by its specific composition, as is known. In apreferred embodiment the catalytically active metal comprises cobalt andmolybdenum. The acidic oxide support or carrier may include silica,alumina, silica-alumina, silica-alumina-phosphates, titania, zirconia,vanadia, and other Group II, IV, V or VI oxides, as well as Y sieves,such as ultra stable Y sieves. Preferred supports include silica,alumina and silica-alumina and, more preferably silica-alumina in whichthe silica concentration in the bulk support (as opposed to surfacesilica) is less than about 50 wt. %, preferably less than 35 wt. % andmore preferably 15-30 wt. %. As is known, if the support is alumina,small amounts of fluorine or chlorine are often be incorporated into itto increase the acid functionality. However, in the process of theinvention, the use of halogens in the catalyst is to be avoided, toprevent impairing the hydrocarbon synthesis catalyst.

Hydroisomerization can be enhanced by using noble metal containingcatalysts in at least one hydroisomerization zone within the downcomerreactor and non-noble metal containing catalysts in at least one otherhydroisomerization zone within the downcomer reactor.

If temperatures higher than those in the synthesis reactor are employedin the downcomer reactor, a non-noble metal hydroisomerization catalystthat is particularly preferred in the practice of the inventioncomprises both cobalt and molybdenum catalytic components supported onan amorphous, low silica alumina-silica support, and most preferably onein which the cobalt component is deposited on the support and calcinedbefore the molybdenum component is added. This catalyst will containfrom 10-20 wt. % MoO₃ and 2-5 wt. % CoO on an amorphous alumina-silicasupport in which the silica content ranges from 20-30 wt. % of thesupport. This catalyst has been found to have good selectivity retentionand resistance to deactivation by oxygenates typically found inFischer-Tropsch produced waxy feeds. The addition of a copper componentsuppresses hydrogenolysis. The preparation of this catalyst is disclosedin, for example, U.S. Pat. Nos. 5,757,920 and 5,750,819, the disclosuresof which are incorporated herein by reference.

Monolithic catalysts are known for automotive exhausts and for chemicalreactions as is shown, for example, in an article by Crynes, et al.,“Monolithic Froth Reactor: Development of a novel three-Phase CatalyticSystem”, AIChE J, v. 41, n. 2, p. 337-345 (Febuary 1995). A corrugatedtype of monolithic catalyst has even been suggested for Fischer-Tropschhydrocarbon synthesis (GB 2,322,633 A). Basically, monolithic catalystscomprise a ceramic or metal support structure of a desired shape, with acatalyst applied to its surface. The monolith may be a metal foam or maybe prepared from the catalyst composition itself or from the catalystsupport, e.g., molecular sieves, with the catalytic metal(s) depositedonto the monolith support. In this latter case, monolith attrition willstill leave catalyst available for the hydroisomerization reaction.Preferred channel sizes for monoliths are in the range >300 μm and lessthan 600 μm.

Very high strength monolithic catalysts may be fabricated from a metalfoundation, over which is applied a suitable ceramic and then thecatalyst. The catalytic material may be a finished catalyst which hasbeen ground to a small particle size, slurried in an appropriate liquid,such as water or an organic liquid, with the slurry then applied to themonolithic support surface as a wash coat and calcined. It is alsopossible to apply one or more applications of catalytic precursormaterials to the ceramic support by impregnation or incipient wetness,followed by drying and calcining. In the practice of the invention, amonolithic catalyst having a minimal solid cross-sectional areaperpendicular to the fluid flow direction is preferred, to minimize thepressure drop of the fluid flowing across the catalytic surface. Suchcatalysts will not be limited to containing substantially longitudinaland parallel fluid flow channels. However, since pressure drop acrossthe catalyst is important, this must be taken into consideration. Micronsize channel openings or openings on the order of a few microns will notbe large enough for this application but openings generally exceeding300 microns would be acceptable. Suitable catalyst shapes for providinga low pressure drop include an open cell foam structure, andconfigurations having a low cross-sectional area perpendicular to thefluid flow direction may also be used. Such shapes will include, forexample, elongated star shapes, with and without an outer peripheralwall, corrugated constructions, with longitudinal channels parallel tothe fluid flow direction, a honeycomb containing a plurality ofopen-ended flow channels substantially parallel to the fluid flowdirection and the like. Many of these shapes may be extruded from a preceramic paste, dried and then fired to the green or fully fired to thefinal state, to provide the foundation for the catalyst material. Stillfurther, all or some of the monolithic catalysts used in thehydroisomerization zone may be shaped in the form of a low pressure dropstatic mixer, such as a Kenics® static mixer in the form of slightlytwisted or spiral-shaped metal strips. A monolithic catalyst having thisshape may be prepared by applying a ceramic over a twisted metal stripand then applying or forming the catalyst on the ceramic. The advantageof this is to provide more intimate mixing of hydrogen and liquid and toprevent stratification of the gas and liquid flows as they flow downthrough the hydroisomerizing zone.

In the practice of the invention, the hydroisomerization zone in thedowncomer reactor will preferably comprise a plurality of monolithsvertically arrayed on top of each other in the hydroisomerization zone.For example, in the case of a vertical, elongated and substantiallyvertical downcomer conduit, a plurality of cylindrical monoliths may bevertically arranged or arrayed along the vertical axis inside thedowncomer conduit to form the hyroisomerization zone. Thecross-sectional area of the catalyst monoliths perpendicular to thedirection of fluid flow will typically proximate that of the interior ofthe conduit. It is preferred that there be vertical spaces between atleast some of the monoliths, to prevent stratification of the gas andliquid as they flown down through the zone. More preferably, a lowpressure drop static mixer, such as a Kenics® static mixer will beplaced in the space between at least some of the arrays, to insureadequate mixing and remixing of the hydrogen treat gas and slurryliquid, as they flow down through the zone. As mentioned above, some orall of the catalyst monoliths themselves may be in the form of a lowpressure drop static mixer, to insure good mixing and low pressure drop.It is preferred to inject the hydrogen or hydrogen treat gas into thehydroisomerization zone via a plurality of gas injection means,vertically spaced apart along the hydroisomerization zone. This willhelp to reduce the lifting action of the gas and stratification, as wellas insuring good mixing of the downflowing fluid and the hydrogen. Stillfurther, it is more preferred that the hydrogen be injected into suchspaces upstream of one or more low pressure drop static mixers in thehydroisomerization zone, to mix the injected gas into the downflowingliquid at each gas injection point. The invention will be furtherunderstood with reference to FIG. 1.

Referring to FIG. 1, a slurry hydrocarbon synthesis reactor 10 is shownas comprising a cylindrical vessel 12 with a synthesis gas feed line 14at the bottom and a gas product line 16 at the top. A synthesis gascomprising a mixture of H₂ and CO is introduced into the plenum space 22at the bottom of the vessel via feed line 14, and then injected upthrough a gas injection means briefly illustrated by dashed line 18 andinto the slurry body 20, which comprises bubbles of the uprisingsynthesis gas, and vapor and gas products of the synthesis reaction,along with solid particles of a Fischer-Tropsch catalyst in ahydrocarbon slurry liquid which comprises synthesized hydrocarbons thatare liquid at the temperature and pressure in the reactor. Suitable gasinjection means comprises a plurality of gas injectors horizontallyarrayed across and extending through an otherwise gas and liquidimpermeable, horizontal tray or plate, as is disclosed for example, inU.S. Pat. No. 5,908,094 the disclosure of which is incorporated hereinby reference. The H₂ and CO in the slurry react in the presence of theparticulate catalyst to form predominantly paraffinic hydrocarbons, mostof which are liquid at the reaction conditions, particularly when thecatalyst includes a catalytic cobalt component. Unreacted synthesis gasand gas products of the hydrocarbon synthesis reaction rise up and outthe top of the slurry and into the gas collection space 24 in the top ofthe reactor, from where they are removed from the hydrocarbon synthesisreactor as tail gas via line 16. A filter means immersed in the slurry,which is simply indicated by box 26, separates the hydrocarbon liquidsin the reactor from the catalyst particles and passes the synthesizedand hydroisomerized hydrocarbon liquid out of the reactor via line 28.Filter 26 may be fabricated of sintered metal, wound wire and the liketo separate the liquid product from the particulate solids in theslurry, and the slurry liquid removed via line 28 is typically sent tofurther processing or sold as a highly refined syncrude of reduced pourpoint. Not shown is means for overhead removal and replacement of thefilter. Downcomer reactor 30 is shown as a vertical, hollow fluidconduit wholly immersed in the surrounding slurry body 20, with its opentop and bottom opening into the surrounding slurry body. While only onesuch downcomer reactor is shown for convenience, a plurality of suchreactors may be employed in the slurry body. The fluid entrance todowncomer 30 comprises a gas disengaging means 32, in the form of anupwardly opening cup which opens upward into the top of slurry body 20.This could be a simple gas bubble disengaging cup as is disclosed inU.S. Pat. No. 5,382,748. Means 32 is wholly immersed in the slurry bodyand is located in the upper portion of the slurry, to maximize thehydraulic head of the gas bubble reduced slurry entering into 30 andalso because the catalyst concentration in the slurry body is typicallylowest at the top. While only a is simple gas bubble removing means isillustrated for the sake of simplicity, it is preferred that both gasbubbles and particulate solids be removed from the slurry, before itpasses down through 30. Simple gas, and preferably gas and solidsdisengaging means, such as those disclosed in the '621 and '537 patentsreferred to above are preferred to means such as conventional filters,magnetic or centrifugal solids separating means, because they do notrequire pumps or expensive equipment. They also provide adensity-difference hydraulic head by virtue of densifying the slurry dueto gas bubble removal, to circulate the slurry from the top of thesurrounding slurry body down into and out of the bottom of the downcomerreactor. The gas reduced and preferably the gas and solids reducedslurry formed in 32 passes down through the interior of downcomerreactor 30, in which it mixes and reacts with hydrogen in the presenceof a series of monolithic hydroisomerizing catalyst sections 34, whichdefine the hydroisomerization zone in the interior of downcomer reactor.The hydrogen or hydrogen treat gas is injected into the interior of thedowncomer reactor, via multiple hydrogen treat gas injection lines 38,just upstream of each successive downstream catalyst section. Typicallyand preferably, the hydroisomerization zone comprises a plurality ofmonolithic catalyst sections or zones, shown as three in the Figure forthe sake of illustration. Each section 34 comprises one or more discretemonolithic catalyst bodies vertically stacked above each other, witheach section vertically spaced apart to permit the hydroisomerizationhydrogen gas injected upstream of each stage, to mix with thedownflowing liquid prior to contact with the downstream catalystsection. Multiple injection of the hydrogen treat gas provides mixing ofthe hydrogen with the downflowing liquid, before each of the threehydroisomerization stages shown, reduces gas/liquid stratification andalso reduces the lifting effect of the injected gas, which tends tooppose the hydraulic downflow circulation of the slurry through 30, tobe significantly less than it would otherwise be if all of the hydrogenwas injected into the downcomer at one point. During thehydroisomerization, a portion of the hydrogen is consumed. Thus,multiple hydrogen injection points vertically spaced apart along thevertical axis of the hydroisomerization zone minimize the lifting effectof the gas and provide more efficient gas/liquid mixing. Also shown inFIG. 1 is a low pressure drop static mixer 36, such as Kenics® staticmixers comprising twisted strips of sheet metal, located in the verticalspace between each catalyst section. One or more such static mixers islocated downstream of each hydrogen injection point and upstream of thenext, successive catalyst section to mix and remix the hydrogen gas withthe downflowing slurry before it enters the next catalyst section. Asimple baffle 40 is located vertically under the slurry exit of 30 asshown, to prevent uprising bubbles of synthesis gas from entering upinto the downflow reactor. It also imparts a horizontal flow componentto the downflowing slurry, as indicated by the two arrows, to providebetter mixing of the hydroisomerized slurry with the surrounding slurrybody. The extent of the hydrocarbon liquid hydroisomerization per passthrough the loop, will vary with the type of catalyst, the amount ofcatalytic surface area, reaction conditions, hydrogen gas andhydrocarbon liquid flow rate, the amount of residual water and CO, ifany, remaining in the liquid, the concentration of normal paraffiniccomponents in the hydrocarbon liquid, etc. The hydrocarbon liquidflowing out of the hydroisomerization reaction zone comprises a mixtureof normal paraffins and hydroisomerized components of reduced pourpoint. If desired, a portion of the downflowing hydroisomerized slurrymay be removed from 30 by means not shown and passed out of thesynthesis reactor to downstream facilities and processing. Also shown inthis embodiment is a catalyst support rod 42, connected to themonolithic catalyst sections and static mixers in the hydroisomerizingzone in the downcomer 30. This permits the monolithic catalyst bodiesand static mixers to be removed for replacement and maintenance througha port or conduit 44, at the top of the synthesis reactor 10. Aremovable plate 48 is detachably attached to 44 via bolts (not shown)that go through flange 46.

It is known that in a Fischer-Tropsch hydrocarbon synthesis process,liquid and gaseous hydrocarbon products are formed by contacting asynthesis gas comprising a mixture of H₂ and CO with a Fischer-Tropschcatalyst, in which the H₂ and CO react to form hydrocarbons undershifting or non-shifting conditions and preferably under non-shiftingconditions in which little or no water gas shift reaction occurs,particularly when the catalytic metal comprises Co, Ru or mixturethereof. Suitable Fischer-Tropsch reaction types of catalyst comprise,for example, one or more Group VIII catalytic metals such as Fe, Ni, Coand Ru. In one embodiment the catalyst comprises catalytically effectiveamounts of Co and one or more of Ru, Fe, Ni, Th, Zr, Hf, U, Mg and La ona suitable inorganic support material, preferably one which comprisesone or more refractory metal oxides. Preferred supports for Cocontaining catalysts comprise titania, particularly when employing aslurry HCS process in which higher molecular weight, primarilyparaffinic liquid hydrocarbon products are desired. Useful catalysts andtheir preparation are known and illustrative, but nonlimiting examplesmay be found, for example, in U.S. Pat. Nos. 4,568,663; 4,663,305;4,542,122; 4,621,072 and 5,545,674. Fixed bed, fluid bed and slurryhydrocarbon synthesis processes are well known and documented in theliterature. In all of these processes the synthesis gas is reacted inthe presence of a suitable Fischer-Tropsch type of hydrocarbon synthesiscatalyst, at reaction conditions effective to form hydrocarbons. Some ofthese hydrocarbons will be liquid, some solid (e.g., wax) and some gasat standard room temperature conditions of temperature and pressure of25° C. and one atmosphere, particularly if a catalyst having a catalyticcobalt component is used. Slurry Fischer-Tropsch hydrocarbon synthesisprocesses are often preferred because they are able to producerelatively high molecular weight, paraffinic hydrocarbons when using acobalt catalyst. In a slurry hydrocarbon synthesis process, which is apreferred process in the practice of the invention and preferably onethat is conducted under nonshifting conditions, a synthesis gascomprising a mixture of H₂ and CO is bubbled up as a third phase througha slurry in a reactor which comprises a particulate Fischer-Tropsch typehydrocarbon synthesis catalyst dispersed and suspended in a slurryliquid comprising hydrocarbon products of the synthesis reaction whichare liquid at the reaction conditions. The mole ratio of the hydrogen tothe carbon monoxide may broadly range from about 0.5 to 4, but is moretypically within the range of from about 0.7 to 2.75 and preferably fromabout 0.7 to 2.5. The stoichiometric mole ratio for a Fischer-Tropschreaction is 2.0, but in the practice of the present invention it may beincreased to obtain the amount of hydrogen desired from the synthesisgas for other than the hydrocarbon synthesis reaction. In the slurryprocess, the mole ratio of the H₂ to CO is typically about 2.1/1. Slurryhydrocarbon synthesis process conditions vary somewhat depending on thecatalyst and desired products. Typical conditions effective to formhydrocarbons comprising mostly C₅₊ paraffins, (e.g., C₅₊-C₂₀₀) andpreferably C₁₀₊ paraffins in a slurry process employing a catalystcomprising a supported cobalt component include, for example,temperatures, pressures and hourly gas space velocities in the range offrom about 320-600° F., 80-600 psi and 100-40,000 V/hr/V, expressed asstandard volumes of the gaseous CO and H₂ mixture (60° F., 1 atm) perhour per volume of catalyst, respectively.

The hydrocarbons which are liquid at the synthesis reaction conditionsand which comprise the slurry liquid which is hydroisomerized by thepractice of the invention, are typically fractionated, with one or moreof the resulting fractions receiving one or more additional conversionoperations. By conversion is meant one or more operations in which themolecular structure of at least a portion of the hydrocarbon is changedand includes both noncatalytic processing (e.g., steam cracking), andcatalytic processing in which a fraction is contacted with a suitablecatalyst, with or without the presence of hydrogen or other coreactants.If hydrogen is present as a reactant, such process steps are typicallyreferred to as hydroconversion and include, for example, furtherhydroisomerization, hydrocracking, hydrorefining and the more severehydrorefining referred to as hydrotreating. Illustrative, butnonlimiting examples of suitable products formed by upgrading includeone or more of a synthetic crude oil, liquid fuel, olefins, solvents,lubricating, industrial or medicinal oil, waxy hydrocarbons, nitrogenand oxygen containing compounds, and the like. Liquid fuel includes oneor more of motor gasoline, diesel fuel, jet fuel, and kerosene, whilelubricating oil includes, for example, automotive, jet, turbine andmetal working oils. Industrial oil includes well drilling fluids,agricultural oils, heat transfer fluids and the like.

The invention will be further understood with reference to the Examplesbelow.

EXAMPLES Example 1

Four bifunctional monolithic hydroisomerization catalysts, eachconsisting of an acidic cracking component and ahydrogenation/dehydrogenation metal component, were prepared usingcylindrically shaped and commercially available, open cell alpha aluminafoam as the monolith support. The alumina foam cylinders were each 0.5inches in diameter and 1 inch long. Two different cell sizes were used,one having 20 pores per inch (ppi) and the other having 65 ppi. Theaverage pore sizes were about 1000 μm and 300 μm. Two different zeoliteswere used as the acidic components, to make two differenthydroisomerization catalysts. These zeolites were LZY-82 and zeolitebeta. Each zeolite was first impregnated with 0.5 wt. % Pt usingstandard incipient wetness techniques, dried, and calcined at 400° C.for 4 hours. The zeolite materials were slurried in water/acetic acid(5%) and then applied onto the alpha alumina foam as washcoats usingmultiple dips followed by calcination (600° C. for 2 hours). The fourfinished monolithic catalysts are summarized in Table 1.

TABLE 1 Monolith Volume Average Loading Catalyst Description in.³ in.³Pt/beta (20 ppi) 0.196 1.82 Pt/beta (65 ppi) 0.196 1.78 Pt/LZY-82 (20ppi) 0.196 1.35 Pt/LZY-82 (65 ppi) 0.196 1.67

Example 2

These four catalysts were evaluated for their hydroconversioneffectiveness for heavy, waxy, paraffinic hydrocarbons using hexadecane(n-C₁₆H₃₈) as a representative feed for a Fischer-Tropsch synthesizedhydrocarbon liquid. The hydroconversion runs were carried out in asmall, up-flow pilot plant running at a hydrogen pressure and nominaltreat rate of 750 psig and 2500 SCF/B with weight hourly space velocity(WHSV) ranging from 2.3 to 3.1. The degree of conversion was varied byadjusting the temperature from 400-550° F. Each reactor was charged with5 of the cylindrical catalytic monoliths in series with alpha aluminafoams of similar ppi rating used at the front and back of the reactionzone. The reactor conditions for each run are summarized in Table 2.

TABLE 2 Feedstock Hexadecane Hexadecane Hexadecane Hexadecane 0.5 wt. %0.5 wt. % 0.5 wt. % 0.5 wt. % Catalyst Pt/Beta Pt/Beta Pt/LZY Pt/LZYDescription (20 ppi) (65 ppi) (20 ppi) (20 ppi) Conditions WHSV, g/hr/g2.3 2.4 3.1 2.5 Temp., ° F. 400-500 H₂ rate, SCF 2500 Feed, grs/hr 4.1

The results of the runs are shown in FIGS. 2 and 3. FIG. 2 is a plot ofhexadecane conversion as a function of temperature, using the Pt/Betacatalysts. FIG. 3 is a plot of the selectivity of the hexadecaneconversion to C₁₆ isoparaffins, determined by gas chromatography, as afunction of the reactor temperature for the Pt/Beta catalysts. Theresults for the Pt/LZY-82 catalysts are not shown, because this catalystwas essentially inactive, even at the relatively high temperature of550° F. The results for the Pt/Beta catalysts shown in FIG. 3 clearlydemonstrate the conversion of the hexadecane to isoparaffin. While thecracking activity of the catalysts was greater than desired, the resultsnevertheless demonstrate the efficacy of hydroisomerizing n-paraffins toisoparaffins, using a monolithic hydroisomerization catalyst.

It is understood that various other embodiments and modifications in thepractice of the invention will be apparent to, and can be readily madeby, those skilled in the art without departing from the scope and spiritof the invention described above. Accordingly, it is not intended thatthe scope of the claims appended hereto be limited to the exactdescription set forth above, but rather that the claims be construed asencompassing all of the features of patentable novelty which reside inthe present invention, including all the features and embodiments whichwould be treated as equivalents thereof by those skilled in the art towhich the invention pertains.

What is claimed is:
 1. A process for hydroisomerizing the slurryhydrocarbon liquid produced in a slurry hydrocarbon synthesis reactor insaid reactor while it is producing said liquid from a synthesis gas andwherein said slurry in said synthesis reactor comprises gas bubbles andcatalyst particles in said liquid, said process comprising: (a)contacting a portion of said slurry with means for removing gas bubbles,to produce a gas bubble reduced slurry having a density greater thanthat of said slurry in said synthesis reactor; (b) passing a hydrogentreat gas and said densified, gas bubble reduced slurry into and downthrough a hydroisomerization zone in one or more downcomer reactorsimmersed in, in fluid communication with and surrounded by said slurryin said synthesis reactor, each said downcomer reactor containing ahydroisomerization catalyst therein which defines a hydroisomerizationzone; (c) reacting said gas bubble reduced slurry and hydrogen in thepresence of said hydroisomerization catalyst, at reaction conditionseffective to hydroisomerize at least a portion of said liquid andproduce a hydroisomerized liquid, and (d) passing all or a portion ofsaid hydroisomerized hydrocarbon liquid back into said surroundingslurry and thereby forming part of said slurry liquid.
 2. A processaccording to claim 1 wherein there is more than one downcomer reactor.3. A process according to claim 2 wherein at least one downcomercontains noble metal containing hydroisomerization catalyst and whereinat least one other downcomer contains non-noble metal hydroisomerizationcatalyst.
 4. A process according to claim 1 wherein circulation of saidgas bubble reduced slurry down through said downcomer reactor and backinto said surrounding slurry in said synthesis reactor is produced atleast in part by density-driven hydraulics due to said slurry densitydifferences.
 5. A process a cording to claim 4 wherein said slurryhydrocarbon liquid is intermittently or continuously withdrawn asproduct liquid from said synthesis reactor, while it is producing saidhydrocarbon slurry liquid.
 6. A process according to claim 5 wherein, inaddition to gas bubble removal, at least a portion of said catalystparticles are also removed from said slurry before it is passed downinto said hydroisomerization zone.
 7. A process according to claim 6wherein said hydroisomerization catalyst comprises a monolithiccatalyst.
 8. A process according to claim 7 wherein saidhydroisomerization catalyst is in the form of a monolith.
 9. A processaccording to claim 7 wherein said monolithic catalyst comprises aplurality of monolithic catalyst bodies vertically arrayed in said zone.10. A process according to claim 9 wherein at least a portion of saidslurry liquid removed from said synthesis reactor is passed to at leastone upgrading operation comprising at least fractionation and/or one ormore conversion operations.
 11. A process according to claim 10 whereinsaid gas bubble removal means is immersed in said slurry in saidsynthesis reactor.
 12. A process according to claim 11 wherein at leasta portion of said monolithic bodies are vertically spaced apart in saidhydroisomerization zone.
 13. A process according to claim 12 whereinsaid hydrogen treat gas is passed into said zone through at least twoseparate gas injection means vertically spaced apart along said zone,each upstream of a monolithic catalyst body.
 14. A process according toclaim 13 wherein a static mixing means is located in at least a portionof said spaces between said monolithic bodies.
 15. A process accordingto claim 14 wherein at least a portion of said hydrogen is injected intosaid hydroisomerization zone upstream of at least one of said mixingmeans.
 16. A process according to claim 5 wherein said gas bubbles andparticulate solids are removed from said slurry by gas bubble and solidsremoving means immersed in said slurry in said synthesis reactor.
 17. Aprocess according to claim 16 wherein said gas bubbles and particulatesolids are removed from said slurry liquid upstream of saidhydroisomerizing zone by density difference.
 18. A process according toclaim 16 wherein said gas bubble removing means is located proximate theslurry entrance of said downcomer reactor.
 19. A slurry hydrocarbonsynthesis process which includes hydroisomerizing hydrocarbon liquidproduced in a slurry hydrocarbon synthesis reactor in one or moredowncomer reactors in said synthesis reactor while it is producing saidliquid from a synthesis gas and wherein said slurry in said synthesisreactor comprises gas bubbles and catalyst particles in said liquid,said process comprising: (a) passing said synthesis gas comprising amixture of H₂ and CO into a slurry body in a slurry Fischer-Tropschhydrocarbon synthesis reactor, in which said slurry body comprises gasbubbles and a particulate hydrocarbon synthesis catalyst in a slurryhydrocarbon liquid; (b) reacting said H₂ and CO in the presence of saidcatalyst at reaction conditions effective to form hydrocarbons, aportion of which are liquid at said reaction conditions and comprisesaid slurry liquid; (c) contacting a portion of said slurry from saidslurry body with means for removing gas bubbles, to form a gas bubblereduced slurry densified to a density greater than that of said slurrycomprising said slurry body; (d) passing a hydrogen treat gas and saiddensified slurry into and down through a hydroisomerization zone in saidone or more downcomer reactors in which they react in the presence of amonolithic hydroisomerization catalyst to form a hydroisomerizedhydrocarbon liquid of reduced pour point, wherein said one or moredowncomer reactors are immersed in said slurry body and wherein saiddensified slurry passes down through said one or more downcomerreactors, at least in part by density-driven hydraulics due to saidslurry density difference, and (e) passing at least a portion of saidhydroisomerized hydrocarbon liquid back into said surrounding slurrybody with which it mixes.
 20. A process according to claim 19 whereinsaid slurry hydrocarbon liquid is intermittently or continuouslywithdrawn as product liquid from said synthesis reactor, while it isproducing said hydrocarbon slurry liquid and wherein at least a portionof said product liquid is passed to at least one upgrading operationcomprising at least fractionation and/or one or more conversionoperations.
 21. A process according to claim 20 wherein said gas bubblereducing means is at least partly immersed in said slurry body.
 22. Aprocess according to claim 21 wherein said monolithic hydroisomerizationcatalyst comprises a plurality of vertically arrayed monolithic catalystbodies, at least a portion of which are vertically spaced apart.
 23. Aprocess according to claim 22 wherein said hydrogen treat gas is passedinto said zone by at least two separate gas injection means verticallyspaced apart along said zone, each upstream of a monolithic catalystbody.
 24. A process according to claim 23 wherein solid particles arealso removed from said slurry, before said slurry liquid contacts saidhydroisomerization catalyst and wherein said gas bubbles and particulatesolids are removed from said slurry by gas bubble and solids removingmeans at least partially immersed in said slurry body.
 25. A processaccording to claim 24 wherein a static mixing means is located in atleast a portion of said spaces between said catalyst bodies.